Considering that radioactive interstitial implants (brachytherapy) are assuming an increasing role in cancer therapy, their effects on normal tissues are not as well understood as they ought to be. Iodine-125 and Iridium-192 are two radionuclides utilized for head and neck cancer therapy and for therapy of other sites and produce very high local tumor control rates. Since primary or recurrent tumors involving the carotid artery present such a formidable challenge, it is natural that interstitial implant techniques have been adopted to produce cures in humans. This project seeks to determine the safety of interstitial implants in the carotid artery in different situations simulating human presentations. Dogs will undergo surgery simulating the defect produced by a radical neck dissection and then the carotid artery will be implanted with either Iodine-125 (7,500-30,000 rad) or Iridium-192 (3,000-12,000 rad). Baseline and follow-up angiography will be done to determine the functional outcome and correlated with necropsy findings at one year. Three other conditions simulating commonly encountered human presentations will be studied. The results should have application to the preparation of implants used for other sites. Data analysis will be performed via the Stanford Center for Information Processing IBM/30/168 computer utilizing the program language SPSS, version 7.2.